Classifications

• • H—ELECTRICITY
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  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
  • H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
• • H—ELECTRICITY
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  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
  • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
  • H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K13/00—Etching, surface-brightening or pickling compositions
  • C09K13/04—Etching, surface-brightening or pickling compositions containing an inorganic acid
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
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  • C09K13/00—Etching, surface-brightening or pickling compositions
  • C09K13/04—Etching, surface-brightening or pickling compositions containing an inorganic acid
  • C09K13/06—Etching, surface-brightening or pickling compositions containing an inorganic acid with organic material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
  • H01L29/76—Unipolar devices, e.g. field effect transistors
  • H01L29/772—Field effect transistors
  • H01L29/78—Field effect transistors with field effect produced by an insulated gate
  • H01L29/786—Thin film transistors, i.e. transistors with a channel being at least partly a thin film
  • H01L29/7869—Thin film transistors, i.e. transistors with a channel being at least partly a thin film having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
  • H01L29/78693—Thin film transistors, i.e. transistors with a channel being at least partly a thin film having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate the semiconducting oxide being amorphous
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/0224—Electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/0224—Electrodes
  • H01L31/022466—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers
  • H01L31/022475—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers composed of indium tin oxide [ITO]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/0224—Electrodes
  • H01L31/022466—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers
  • H01L31/022483—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers composed of zinc oxide [ZnO]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/547—Monocrystalline silicon PV cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the present invention relates to an etching method of an oxide film containing In, Ga, and Zn with a high selectivity with respect to ITO (Indium Tin Oxide) . More specifically, the present invention relates to a highly selective etching method of an oxide containing In and Zn and an oxide containing In and Ga which is employed in producing a fine electronic component such as a semiconductor device, a semiconductor integrated circuit, and an electrode.
• ITO Indium Tin Oxide
• oxide films containing In, Ga, and Zn are optically transparent, and are also widely studied for application to transparent electrodes, transistors, and the like by reducing the resistance.
• H. M. Kim et al., Jpn . J.Appl. Phys . Vol. 42, 2003, p.223-227 and R. E. Presley et al., Vol. 50, Issue 3, March 2006, p.500-503 disclose that reports have been made on researches on oxide films containing In and Zn or oxide films containing In and Ga.
• an oxide film containing In, Ga, and Zn is hereinafter referred to as IGZO.
• an oxide film containing In and Zn is hereinafter referred to as IZO.
• IGO oxide film containing In and Ga
• ITO indium-tin oxide
• etching liquid oxalic acid, a mixed acid of phosphoric acid, acetic acid, and nitric acid, an aqueous cerium ammonium nitrate solution, or the like is used as an etching liquid
• the lift-off process as described above has a problem that a photoresist is melted and deformed at a high temperature.
• the lift-off process has another problem that when a photoresist is removed, an edge of a pattern of a deposited film is curved up, and thereafter an electric wire crossing over the pattern edge is liable to be broken, which lowers the production yield.
• the oxide film containing In, Ga, and Zn needs to be processed. Therefore, in order to achieve a desired shape with high reproducibility, various etchingmethods have been studied as a patterning method other than the lift-off process.
• the etching method is roughly classified into two methods .
• the dry etching method has an advantage that chemically active ions generated in a plasma bombard vertically on the surface of the substrate, so that the etched shape is faithfully transferred from the mask pattern.
• maintenance costs for a dry- etching apparatus body, a circumferential gas supply system, exhaust gas processing of a chlorine-based gas, power consumption and the like are remarkably large, and there is also a problem of short life of the apparatus due to particle contamination or the like . Further, there is a case where the control of highly selective etching is difficult due to ion impact.
• the wet etching proceeds isotropically, so that there arises a problem of generating a phenomenon such as an undercut beneath a mask.
• the wet etching has an advantage that the apparatus cost is significantly reduced compared with the dry etching.
• the wet etching is considered to be suitable for mass production because of its ease of control and management of concentration and temperature conditions of an etching liquid (also referred to as "etchant").
• the selectivity of an etching liquid to an ITO electrode is very important.
• the composition of the oxide and the film deposition conditions can be adjusted to obtain a large change in the electrical conductivity. Therefore, there can be adopted a stack structure in which a semiconductor active layer, a high-conductivity electrode layer, and wiring are formed by using only the transparent oxides such as IGZO, IZO, and IGO without using ITO. Therefore, in the case of producing a device using only the transparent oxides such as IGZO, IZO, and IGO without using ITO, the etch selectivity of these oxides becomes a major subject. If the etch selectivity is insufficient, there are cases where a material not to be etched may be etched, which may increase variation in the performance of electronic devices, thus resulting in reduction of the yield.
• the present invention has been accomplished to solve the above-mentioned problems. That is, the present invention provides a method of etching a structure in which IZO and ITO, IGZO and ITO, IGO and ITO, IZO and IGZO, IZO and IGO, or IGZO and IGO coexist. More specifically, the present invention provides an etching method of performing selective etching by using an etching liquid having selectivity for different substances. The present invention also provides an etching method by which precise and easy etching can be performed in a thin film semiconductor device containing two or more kinds of oxide films selected from IGZO, IZO, IGO, and ITO.
• the present inventor has conducted extensive study on the deposition conditions and etching conditions of films containing IGZO, IZO, or IGO, and thin film semiconductor devices using such films. As a result, the present inventor has found that a layer structure including two or more kinds of indium oxide films selected from IGZO, IZO, IGO, and ITO can be selectively etched by using a etching liquid containing any one of acetic acid, organic acid, hydrochloric acid, or perchloric acid.
• the present invention has been accomplished based on the above-mentioned finding and provides an etching method of an amorphous oxide layer containing In and at least one of Ga and Zn, which includes etching the amorphous oxide layer using an etching liquid containing any one of acetic acid, citric acid, hydrochloric acid, and perchloric acid.
• the present invention provides an etching method of an amorphous oxide layer containing In and at least one of Ga and Zn in a structure including an ITO layer and the amorphous oxide layer, which includes selectively etching the amorphous oxide layer using an etching liquid containing any one of acetic acid, citric acid, hydrochloric acid, and perchloric acid.
• the present invention provides an etching method of an amorphous oxide layer containing In and Zn, or In, Ga, and Zn in a structure including an oxide layer containing In and Ga and the amorphous oxide layer, which includes selectively etching the amorphous oxide layer using an etching liquid containing any one of acetic acid, citric acid, hydrochloric acid, and perchloric acid.
• the present invention provides an etching method of an amorphous oxide layer containing In and Zn in a structure including an oxide layer containing In, Ga, and Zn and the amorphous oxide layer, which includes selectively etching the amorphous oxide layer using an etching liquid containing any one of acetic acid, citric acid, hydrochloric acid, and perchloric acid.
• the thin film semiconductor device including two or more kinds of oxide films selected from IGZO, IZO, IGO, and ITO.
• the thin film semiconductor device produced by the etching method of the present invention and by using the etching liquid having remarkable selectivity of the present invention is advantageous in that the device performance is not variable and is stabile and uniform, and that the device productions steps are simple and easy to carry out.
• FIG. 1 is a graphical representation illustrating acetic acid concentration dependence of an etch rate of an indium oxide film, for explaining an etching liquid containing acetic acid according to Example 1 of the method of the present invention
• FIG. 2 is a graphical representation illustrating acetic acid concentration dependence of an etch selectivity of an indium oxide film to ITO, for explaining an etching liquid containing acetic acid according to
• FIG. 3 is a graphical representation illustrating room temperature citric acid concentration dependence of an etch rate of an indium oxide film, for explaining an etching liquid containing citric acid according to Example
• FIG. 4 is a graphical representation illustrating room temperature citric acid concentration dependence of an etch selectivity of an indium oxide film to ITO, for explaining an etching liquid containing citric acid according ⁇ to Example 1 of the method of the present invention
• FIG. 5 is a graphical representation illustrating citric acid concentration dependence at 50°C of an etch rate of an indium oxide film, for explaining an etching liquid containing citric acid according to Example 1 of the method of the present invention
• FIG. 6 is a graphical representation illustrating citric acid concentration dependence at 50°C of an etch selectivity of an indium oxide film to ITO, for explaining an etching liquid containing citric acid according to Example 1 of the method of the present invention
• FIG. 7 is a graphical representation illustrating hydrochloric acid concentration dependence of an etch rate of an indium oxide film, for explaining an etching liquid containing hydrochloric acid according to Example 1 of the method of the present invention
• FIG. 8 is a graphical representation illustrating hydrochloric acid concentration dependence of an etch selectivity of an indium oxide film ' to ITO, for explaining an etching liquid containing hydrochloric acid according to Example 1 of the method of the present invention
• FIG. 9 is a graphical representation illustrating perchloric acid concentration dependence of an etch rate of an indium oxide film, for explaining an etching liquid containing perchloric acid according to Example 1 of the method of the present invention.
• FIG. 10 is a graphical representation illustrating perchloric acid concentration dependence of an etch selectivity of an indium oxide film to ITO, for explaining an etching liquid containing perchloric acid according to Example 1 of the method of the present invention
• FIG. HA is a schematic cross-sectional view of a layer structure before etching, for explaining an etching method according to Example 2 of the method of the present invention
• FIG. HB is a schematic cross-sectional view of the layer structure after the etching, for explaining the etching method according to Example 2 of the method of the present invention
• FIG. 12 is a schematic cross-sectional view illustrating a layer structure of a top-gate bottom-contact TFT according to Example 3 of the method of the present invention
• FIG. 13 is a schematic cross-sectional view illustrating a layer structure of a bottom-gate top-contact TFT according to Example 4 of the method of the present invention
• FIGS. 14A, 14B, 14C, 14D, 14E, 14F, 14G, 14H, 141, 14J, and 14K are schematic cross-sectional views illustrating production steps of the top-gate bottom-contact TFT according to Example 3 of the method of the present invention.
• FIGS. 15A, 15B, 15C, and 15D are schematic cross-sectional views illustrating the bottom-gate top-contact TFT according to Example 4 of the method of the present invention.
• etching can be precisely controlled when producing a device in which different kinds (or a plurality) of indium oxides coexist .
• the specific material to be etched include those having a structure in which IZO and ITO, IGZO and ITO, IGO and ITO, IZO and IGZO, IZO and IGO, or IGZO and IGO coexist.
• an etching liquid for etching such a structure, an etching liquid can be obtained which has selectivity for different substances.
• acetic acid for use in the present invention commercially available acetic acid liquid (100% by weight of glacial acetic acid; density of 1.05; hereinafter referred to as "stock solution") may be used as such, or may be diluted with pure water in an amount up to 4 times the volume of the stock solution and then used.
• stock solution acetic acid liquid
• the etching process using the acetic acid is performed by immersing an etching object in an aqueous acetic acid solution at room temperature (about 20°C) .
• organic acids are described.
• Usable organic acids are not limited to citric acid, and examples thereof include any generally known organic acids, such as malonic acid, malic acid, tartaric acid, oxalic acid, formic acid, glycolic acid, and maleic acid.
• a ligand existing in an organic acid, for example, COO is combined with In to form a complex ion under specific conditions and is dissolved.
• citric acid is a solution prepared by dissolving commercially available citric acid (citric acid monohydrate; chemical formula: CsH 4 (OH) (COOH) 3 -H 2 O; white solid crystal) in pure water completely .
• the citric acid concentration of an etching liquid containing citric acid of room temperature is desirably 3.8% by weight or more and 45% by weight or less.
• the citric acid concentration is more desirably 3.8% by weight or more and 29% by weight or less.
• the citric acid concentration is less than 3.8% by weight, the etch rates of all oxides containing indium are lowered, so that the etch selectivity is remarkably reduced.
• the citric acid concentration is more than 45% by weight, there are cases where citric acid crystals may be precipitated in an aqueous etching solution containing citric acid.
• the temperature of the etching liquid containing citric acid is desirably within the range of 20 0 C or more and 55°C or less, and more desirably within the range of 40 0 C or more and 55°C or less.
• the aqueous citric acid solution is at about 50 0 C, the etch selectivities of the indium oxides including IZO, IGZO, and IGO to ITO do not significantly change, but the etch rate increases by approximately one order of magnitude from that at room temperature.
• a unit for cooling, condensing, and collecting water that has evaporated from the etching liquid needs to be provided.
• the citric acid concentration of the etching liquid containing citric acid of 50 0 C be within the range of 3.8% by weight or more and 45% by weight orless.
• the citric acid concentration of the etching liquid containing citric acid at a temperature within the range of room temperature to 55°C be within the range of 16% by weight or more and 29% by weight or less.
• the etch selectivities of the indium oxides including IZO, IGZO, and IGO with respect to ITO are the highest and stable, without depending on the etching liquid temperatures.
• hydrochloric acid commercially available concentrated hydrochloric acid (containing 37.2'% by weight of hydrogen chloride and having a density of 1.18, which will hereinafter be referred to as "stock solution") may be used as such or may be diluted with pure water in an
• the hydrochloric acid stock solution used for the etching liquid be diluted with pure water in an amount 4 to 60 times the volume of the stock solution (concentration:
• the stock solution be diluted with pure water in an amount 4 to 40 times the volume of the stock solution (concentration: 1.0% by weight or more and
• the most desirable hydrochloric acid concentration is obtained by diluting the stock solution with pure water in an amount 10 to 30 times the volume of the stock solution (concentration: 1.4% by weight or more and 4.0% by weight or less) .
• the etching process using hydrochloric acid is performed through immersion in an aqueous hydrochloric acid solution of room temperature
• perchloric acid commercially available concentrated perchloric acid solution (concentration: 70% by weight; chemical formula: HCIO 4 ; density: 1.673; hereinafter referred to as "stock solution”) may be used as such or may be diluted with pure water in an amount 20 or less times the volume of the stock solution.
• stock solution concentrated perchloric acid solution
• a desirable perchloric acid concentration is obtained through dilution with pure water in an amount 1 to 20 times the volume of the stock solution (concentration: 5% by weight or more and 44% by weight or less) .
• the most desirable perchloric acid concentration is obtained through dilution with pure water in an amount 2 to 10 times the volume of the stock solution (concentration: 10% by weight or more and 32% by weight or less) .
• concentration: 10% by weight or more and 32% by weight or less concentration: 10% by weight or more and 32% by weight or less.
• the etching process using perchloric acid is performed through immersion in an aqueous perchloric acid solution of room temperature (about 20°C) .
• the etch rates of the indium oxides can be set so as to be IZO > IGZO > IGO > ITO.
• the production yields of semiconductor devices when using the oxide films containing indium, such as IZO, IGZO, and IGO as an active layer and an electrode can be remarkably improved.
• high production yield is important in the case of large area substrates.
• film deposition may be performed in an atmosphere containing oxygen gas without intentionally adding impurity ions for increasing the electric resistance of the oxide thin film containing indium.
• oxygen concentration and the film deposition temperature By adjusting the oxygen concentration and the film deposition temperature, the electric resistance of the oxide containing indium can be adjusted.
• the oxide films containing indium are produced by a thin film deposition process selected from sputtering process, vapor depositionprocess, CVDprocess, epitaxial growth process, photo induced deposition process, pulse laser vapor deposition process, and ion plating process.
• a thin film deposition process selected from sputtering process, vapor depositionprocess, CVDprocess, epitaxial growth process, photo induced deposition process, pulse laser vapor deposition process, and ion plating process.
• the sputtering process is most suitable from the viewpoint of mass productivity.
• the conductivities of the indium oxide films including IZO, IGZO, and IGO strongly depend on temperature ,- it is desirable not to increase the temperature as far as possible in a wet etching process. As the temperature increases, the conductivities of the oxide films containing In, Ga, and Zn increase. Therefore, the above-mentioned wet etching process temperature is desirably set to 60°C or less.
• the resistance of the film can be adjusted by film deposition conditions, so that the oxide film can be utilized not only as an active layer but also as pixel wiring for liquid crystals.
• the material of the oxide film containing indium at least one of impurities such as Sn, Al, Sb, Cd, Ge, P, As, N, and Mg can be added to compounds including IZO, IGZO, and IGO.
• an etching liquid containing a weak acid organic acids such as acetic acid or citric acid
• hydrochloric acid or perchloric acid with a lower concentration. This is because degradation may increase with increase of the etching temperature.
• a substrate is made of a resin such as polyimide, polyethylene terephthalate, or polyethylenenaphthalate, the acid resistance thereof is insufficient. Therefore, it is desirable to use hydrochloric acid or perchloric acid that has been diluted with pure water.
• a desirable hydrochloric-acid concentration at room temperature is obtained by diluting the stock solution with pure water in an amount of 4 to 60 times the volume of hydrochloric acid stock solution. Since immersion in a short period of time is also desirable, a more desirable hydrochloric acid concentration at room temperature is obtained by diluting the stock solution with pure water in an amount 10 to 30 times the volume of hydrochloric acid stock solution .
• a desirable perchloric acid concentration at room temperature is obtained by diluting the stock solution with pure water in an amount 1 to 20 times the volume of perchloric-acid stock solution.
• a more desirable perchloric acid concentration at room temperature is obtained by dilution with pure water in an amount 2 to 10 times the volume of perchloric-acid stock solution.
• the above-mentioned acid etching liquid i.e., solution of any one of acetic acid, organic acid, hydrochloric acid, and perchloric acid
• a gate insulation film such as a silicon nitride film, which is generally used commonly.
• silicon oxide or dielectric materials such as silicon oxynitride, HfO 2 , HfAlO, HfSiON, or Y 2 O 3 can be applied to a TFT device as the gate insulation film without being etched by the above-mentioned acid etching liquid.
• Example 1 Etch Rate Measurement
• Example 1 a specific example of an etching method of an indium oxide film including IZO, IGZO, IGO, and ITO of the present invention will be described.
• experimental samples are produced according to a procedure described below.
• a Si substrate (525 mm in thickness) having a 100 nm thick Si thermal oxide film provided thereon is used as a base.
• Three oxide films of an IGZO film, an IZO film, and an IGO film are formed on theSi substratewiththeSi thermally oxide filmby reactive sputtering under the conditions shown in Table 1 below.
• indium oxide thin films of IGZO, IZO, and IGO each containing microcrystals are deposited on the substrate by the above-mentioned spattering film deposition method.
• the incidence X-ray diffraction (angle of incidence: 0.5°) of the IGZO, IZO, and IGO thin films shows no clear diffraction peak, it can be said that the produced IGZO, IZO, and IGO thin films are amorphous .
• a line-and-space resist pattern with a line width of 100 micron and a space width of 100 micron is formed on the IGZO, IZO, IGO, and ITO thin films by a known photolithography method.
• the resist used is a positive resist AZ1500 (trade name; 20 cp) manufactured by Clariant .
• ASi substrate with the resist is hardbakedat a temperature of about 120°C using a baking furnace to thereby obtain samples for etching experiments.
• the hard bake process is carried out for improving the adhesion of the resist during wet etching to be performed later and the resistance against an etching liquid.
• DI water deionized water
• etching liquid it is desirable to heat the etching liquid in a water bath.
• evaporation from an etching liquid is suppressed by use of a lid, and evaporated water is frequently replenished.
• the resist of each sample is stripped with acetone.
• the patterns of the indium oxide films are measured and observed .
• the step difference produced by the etching is measured with a surface profiler (trade name: Alpha-Step) and ellipsometer manufactured by KLA-Tencor Corporation, and the etch rate is accurately computed.
• FIG. 1 is a graphical representation illustrating the acetic acid concentration dependence of the etch rates of IZO, IGZO, IGO, and ITO when an aqueous acetic acid water solution is used at room temperature (ordinate: etch rate (nm/min) ; abscissa: volume ratio of diluting pure water to acetic acid stock solution) .
• FIG.2 is a graphical representation illustrating the acetic acid concentration dependence of the etch selectivities of IZO, IGZO, and IGO with respect to ITO obtained by converting the data of FIG. 1 (ordinate: etch selectivity to ITO; abscissa: volume ratio of diluting pure water to acetic acid stock solution) . As shown in FIGS.
• the etch rates of the indium oxides can be stably set so as to be IZO > IGZO > IGO > ITO.
• the pure water content of the etching liquid further increases, the etch selectivity is lost and the etch rate is not practical.
• FIG. 3 is a graphical representation illustrating the citric acid concentration dependence of the etch rates of IZO, IGZO, IGO, and ITO when an aqueous citric acid solution is used as an organic acid at room temperature (ordinate: etch rate (nm/min) ; abscissa: % by weight concentration of citric acid) .
• FIG. 4 is a graphical representation illustrating the citric acid concentration dependence of the etch selectivities of IZO, IGZO, and IGO to ITO obtained by converting the data of FIG. 3
• etch selectivity to ITO abscissa: % by weight concentration of citric acid
• Usable organic acids are not limited to citric acid, and usable are any generally known organic acids, such as malonic acid, malic acid, tartaric acid, and oxalic acid.
• Citric acid is used in this example.
• the citric acid concentration of a room-temperature (about 20°C) etching liquid containing citric acid is desirably 3.8% by weight or more and 45% by weight or less.
• the citric acid concentration is desirably 3.8% by weight or more and 29% by weight or less.
• FIG. 5 is a graphical representation illustrating the citric acid concentration dependence at 50 0 C ( ⁇ 5°C) of the etch rates of IZO, IGZO, IGO, and ITO (ordinate: etch rate (nm/min) ; abscissa ⁇ % by weight concentration of citric acid) .
• FIG. 5 is a graphical representation illustrating the citric acid concentration dependence at 50 0 C ( ⁇ 5°C) of the etch rates of IZO, IGZO, IGO, and ITO (ordinate: etch rate (nm/min) ; abscissa ⁇ % by weight concentration of citric acid) .
• FIG. 6 is a graphical representation illustrating the citric acid concentration dependence at 50 0 C of the etch selectivities of IZO, IGZO, and IGO to ITO obtained by converting the data of FIG. 5 (ordinate: etch selectivity to ITO; abscissa: % by weight concentration of citric acid) .
• the etch rates of the indiumoxides including IZO, IGZO, IGO, and ITO increase at near 50°C by approximately one order of magnitude as compared to that at room temperature, and the etch selectivities with respect to ITO also increase slightly. Therefore, in order to make the etch selectivity higher, the temperatures of the etching liquid containing citric acid is desirably 20 0 C or more and 55°C or less, and more desirably 40 0 C or more and 55°C or less. As is seen from in FIGS. 5 and 6, the citric acid concentration of the etching liquid containing citric acid of 50 0 C is desirably 3.8% by weight or more and 45% by weight or less.
• the citric acid concentration of the etching liquid containing citric acid is desirably 16% or more and 45% by weight or less.
• the citric acid concentration of the etching liquid containing citric acid be not less than 16% by weight and not more than 29% by weight within the temperature range of from room temperature to 55°C.
• the etch selectivities of the indium oxide including IZO, IGZO, and IGO to ITO are most stable without depending on the temperature of the etching liquid.
• FIG. 7 is a graphical representation illustrating the hydrochloric acid concentration dependence of the etch rates of IZO, IGZQ, IGO, and ITO when an aqueous hydrochloric acid solution is used at room temperature (ordinate: etch rate (nm/min) ; abscissa: volume ratio of diluting pure water to hydrochloric acid stock solution) .
• etch rate nm/min
• abscissa volume ratio of diluting pure water to hydrochloric acid stock solution
• FIG. 8 is a graphical representation illustrating the hydrochloric acid concentration dependence of the etch selectivities of IZO, IGZO, and IGO to ITO obtained by converting the data of FIG.
• the hydrochloric-acid concentration of the etching liquid containing hydrochloric acid is desirably obtained by- diluting with pure water in an amount 4 to 60 times the volume of the stock solution (concentration: 0.7% by weight or more and 8.5% by weight orless) .
• FIG. 9 is a graphical representation illustrating the perchloric acid concentration dependence of the etch rates of IZO, IGZO, IGO, and ITO when an aqueous perchloric acid solution is used at room temperature (ordinate: etch rate (nm/min) ; abscissa: % by weight concentration of perchloric acid) .
• FIG. 10 is a graphical representation illustrating the perchloric acid concentration dependence of the etch selectivities of IZO, IGZO, and IGO to ITO obtained by converting the data of FIG. 9 (ordinate: etch selectivity to ITO; abscissa: % by weight concentration of perchloric acid) . As is seen from FIGS.
• a desirable perchloric acid concentration is obtained by dilution with pure water in an amount 1 to 20 times the volume of the stock solution (concentration: 5% by weight or more and 44% by weight or less) .
• the etch rate markedly increases by adding pure water of the above-mentioned amount to the stock solution, as compared with that of the stock solution.
• the etch rate tends to be reduced due to an excessive amount of pure water. Therefore, the most desirable perchloric acid concentration is obtained by dilution with pure water in an amount 2 to 10 times the volume of the stock solution (concentration: 10% by weight or more and 32% by weight or less) .
• Example 1 The wet etching experimental results of Example 1 show that the etch rates of the oxides almost stably have the relationship of IZO > IGZO > IGO > ITO. Therefore, it can be seen that in the respective etching liquids, the selectivities of IZO to IGZO, IGZO to IGO, or IGO to ITO are lower than the relative selectivities of other oxides. More specifically, the critical value (minimum etch selectivity) of the etch selective abilities of the above-mentioned etching liquids resides in any one of the three etch selectivities of IZO to IGZO, IGZO to IGO, and IGO to ITO. Table 3 shows the ranges of the selectivities of IZO to IGZO, IGZO to IGO, and IGO to ITO for the respective etching liquids. Table 3
• the selectivities of IGO to ITO are each at leastonedigit value, andallthe aforementioned etching liquids can be applied thereto.
• the use of the room temperature citric acid e.g., citric acid concentration of about 45% by weight
• the use of the citric acid of 50°C e.g., citric acid concentration of about 9% by weight
• the use of the room temperature citric acid e.g., citric acid concentration of about 29% by weight
• the use of the perchloric acid enables to give higher etch selectivity (e.g. , at near perchloric acid concentration of about 70% by weight), and thus is the most desirable.
• the selectivity of the etching liquid varies according to the combination of the material to be etched and a matrix material.
• etching conditions such as etching liquids, concentrations, and temperatures in accordance with the combination of the materials. According to the findings of the present inventor, the following conditions are desirable, for example.
• Citric acid concentration 3.8 to 45% by weight, more desirably 3.8 to 29% by weight; (50°C) Citric acid concentration: 16 to 45% by weight; (Room temperature) Hydrochloric acid concentration: 0.7 to 8.5% by weight (water to hydrochloric acid stock solution: 4 to 60 times), more desirably 1.0 to 8.5% by weight (water to hydrochloric acid stock solution: 4 to 40 times), most desirably 1.4 to 4% by weight (water to hydrochloric acid stock solution: 10 to 30 times); (Room temperature) Perchloric acid concentration: 5 to 44% by weight (water to perchloric acid stock solution: 1 to 20 times) .
• Citric acid concentration 3.8 to 45 % by weight
• Citric-acid concentration 16 to 45 % by weight
• FIGS. HA and HB are cross-sectional views illustrating the most common etching form according to an example of the present invention.
• Alayer 1 is a material layer with a lower etch rate
• a layer 2 is a material layer with a higher etch rate
• a layer 3 resist layer
• the selectivity of the layers 1 and 2 of FIGS. HA and HB is low, the depth of excessively etched area ⁇ d of the layer 1 of FIG.
• the etch rates of oxides containing indium have the relationship of IZO > IGZO > IGO > and ITO.
• the layer 1 of FIGS. HA and HB is an ITO layer and the layer 2 is one material selected from the group consisting of IZO, IGZO, and IGO, there can be obtained the highly selective etching effect such that the etch selectivity of the layer 2 to the layer 1 is of about two digits or more.
• the etch selectivity obtained using citric acid is approximately of one digit.
• the layer 1 of FIGS. HA and HB is an IGO layer and the layer 2 is any one of the two materials of IZO and IGZO, there can also be obtained the highly selective etching effect such that the etch selectivity of the layer 2 to the layer 1 is of about one digit.
• the layer 1 is an IGZO layer and the layer 2 is IZO
• the selective etching of IZO to IGZO can be performed.
• FIG. 12 is a schematic cross-sectional view illustrating a structure of a top-gate bottom-contact thin film transistor according to one example of the present invention.
• Reference numerals 4, 5, 6, 7, 8, and 9 denote a substrate (e.g., glass substrate), drain electrode, source electrode, active layer (channel layer) , gate insulation film, and gate electrode, respectively.
• Reference character L denotes a channel length.
• FIGS. 14A to 14K are schematic cross-sectional views illustrating production steps of a top-gate bottom-contact thin film transistor as shown in FIG.
• Example 12 using the etching liquid of Example 1 of the present invention.
• a glass plate having a thickness of 500 mm (manufactured by Corning; trade name: Corning 1737 glass; glass transition temperature: 640°C) is used as the substrate 4.
• a polycrystalline ITO film with a thickness of 250 nm is formed on the surface of the substrate 4 by reactive sputtering-, and the drain electrode 5 and the source electrode 6 are patterned by dry etching.
• an IGZO oxide film layer having a thickness of 100 nm is formed thereon as the active layer (channel layer) 7 by reactive sputtering.
• the IGZO oxide film includes In-Ga-Zn-O, and the composition in a crystalline state is represented by InGaO 3 (ZnO) m (m is a natural number of less than 6) .
• the transparent IGZO oxide film is a transparent amorphous semiconductor oxide film containing microcrystals therein and having an electron carrier concentration of less than 10 18 /cm 3 .
• FIG.14C illustrates a step of exposing contact pads for wiring of the drain electrode 5 and the source electrode 6 to the surface of the active layer (channel layer) 7 and patterning the resist layer 3 for forming a channel.
• this resist pattern is used as an etching mask, and the above-mentioned active layer (channel layer) 7 is etched with the etching liquid of Example 1 , whereby the contact pads of the drain electrode 5 and source electrode 6 are exposed.
• the present invention enables to perform selective etching of the active layer 7 with respect to the drain electrode 5 and source electrode 6.
• the etch selectivity of IGZO to ITO is about 2000. More specifically, because the etch rate of IGZO is high and the etch rate of ITO is low, the etching can be performed in such a manner that IGZO is greatly etched and ITO is hardly etched. More specifically, as shown in FIG.
• a two-layer structure of the ITO layer 1 and the IGZO layer 2 is etched with the above-mentioned liquid by using the resist 3 as an etching mask, whereby only the IGZO layer 2 is etched and the etching can be precisely stopped at the surface of the ITO layer 1.
• the etching depth d of the active layer can be precisely controlled. More specifically, the above described conventional etching method of indium oxide film have problems of, for example, rise in electrical resistance or damage to the electrode and wiring due to the depth ⁇ d of excessive etching in the drain electrode and source electrode. The present invention can solve the problem of the variation in the device performances.
• FIG. 14E illustrates a step of stripping the resist layer 3 with acetone after the selective etching of the active layer 7.
• FIG. 14F illustrates a step of forming a silicon nitride film (Si 3 N 4 ) having a thickness of 100 nmas the gate insulation film layer 8 by reactive sputtering on the uppermost surface of the upper side of the substrate 4.
• silicon oxide, or dielectric materials such as silicon oxynitride, HfO 2 , HfAlO, HfSiON, and Y 2 O 3 can be used as the gate insulation film layer 8. As shown in FIG.
• the pattern of the gate insulation film layer 8 is formed by photolithography and reactive ion etching (RIE) .
• RIE reactive ion etching
• the silicon nitride film is dry etched using fluorocarbon gas (e.g., CF 4 ). It is known that indium oxides cannot be etched with ions or radicals generated from the fluorocarbon gas by plasma.
• FIG. 14G illustrates an example in which the active layer 7 is entirely covered with the gate insulation film layer 8. However, in this process, the gate insulation film layer 8 does not necessarily have to cover the entire active layer 7, and insulation may be made between the gate electrode layer 9 and the active layer 7 in subsequent steps.
• the gate electrode layer 9 and the active layer 7 can be brought into contact with each other.
• the etch selectivity of the electrode layer 9 with respect to the active layer 7, the drain electrode layer 5, and the source electrode layer 6 may be required in a subsequent step illustrated in FIG. 14J.
• an IZO film having a thickness of 100 nm is formed as the gate electrode layer 9 by reactive sputtering on the top surface of the upper side of the substrate 4.
• a pattern is formed on the gate electrode layer 9 using the resist layer 3 as an etching mask by photolithography.
• the gate electrode layer 9 is etched using an etching liquid containing citric acid to form the gate electrode 9.
• An etching liquid in which the weight ratio of citric acid crystal powders to pure water is 40:100 (concentration: 28.6% by weight) is used at room temperature (about 20 0 C) .
• the etch selectivity of IZO to IGZO is about 14.8, and the etch selectivity of IZO to
• ITO is about 1400. That is, also in the case where the active layer 7 is exposed from the gate insulation layer 8 using the etching liquid containing citric acid, selective etching of the gate electrode layer 9 (IZO) to the active layer (IGZO) and simultaneously to the drain electrode layer 5 (ITO) and the source electrode layer 6 (ITO) can be performed.
• a hydrochloric acid solution mole concentration: 6 M
• the etch selectivity of IZO to the IGZO is as low as about 1.06, and selective etching of the gate electrode layer 9 (IZO) to the active layer (IGZO) cannot be performed.
• FIG. 13 is a schematic cross-sectional view illustrating a structure of a bottom-gate top-contact thin film transistor according to another embodiment of the present invention.
• Reference numerals 4, 5, 6, 7, 8, and 9 denote a substrate (e.g., glass substrate), drain electrode, source electrode, active layer (channel layer) , gate insulation film, and gate electrode, respectively.
• Reference character L denotes a channel length.
• FIGS.15A, 15B, 15C, and 15D are schematic cross-sectional views illustrating production steps of a bottom-gate top-contact thin film transistor as shown in FIG. 13 using the etching liquid of Example 1 of the present invention.
• gate electrode layer 9 having a film thickness of 100 nm is formed by reactive sputtering on the surface of a glass plate with a thickness of 500 mm (manufactured by
• a resist is patterned on the surface of the gate electrode layer 9 (IGO) as an etching mask by photolithography.
• the gate electrode layer 9 (IGO) is patterned with dilute hydrochloric acid etching liquid having a concentration of 4.0% by weight and the resist is stripped.
• a silicon nitride film (Si 3 N 4 ) having a film thickness of 100 nm formed by reactive sputtering is patterned as the gate insulation film 8 on the surface of the gate electrode layer 9 by photolithography and dry etching.
• Si 3 N 4 silicon nitride film having a film thickness of 100 nm formed by reactive sputtering
• FIG. 15A is a schematic cross-sectional view illustrating the state in which the resist has been stripped after the dry etching .
• silicon oxide or dielectric materials such as silicon oxynitride, HfO 2 , HfAlO, HfSiON, and Y 2 O 3 can be used as the gate insulation film layer 8.
• the gate electrode 9 is not completely covered with the gate insulation film 8 but a part of the gate electrode 9 needs to be exposed as a contact pad.
• the contact pad of the gate electrode 9 is provided in a direction perpendicular to the drawing plane of FIG. 15A, but is not shown in FIG. 15A.
• an IGZO layer having a film thickness of 100 nm is formed thereon as the active layer (channel layer) 7 by reactive sputtering.
• the IGZO oxide film includes In-Ga-Zn-O, and the composition thereof in a crystalline state is represented by InGa ⁇ 3 (ZnO)m (mis a natural number of less than 6) .
• the IGZO oxide film is a transparent amorphous semiconductor oxide containing microcrystals therein and having an electron carrier concentration of less than 10 18 /cm 3 .
• the resist layer 3 is patterned on the surface of the active layer 7 (IGZO) as an etching mask by photolithography.
• the etch selectivity of IGZO to IGO is about 21.8, so that selective etching can be performed. That is, as shown in FIG. 15B, even if a part of the contact pad of the gate electrode 9 (IGO) is actually exposed using the etching liquid containing citric acid, selective etching of the active layer 7 (IGZO) can be performed. In this case, if an etching liquid having no selectivity is used, the gate electrode 9 is etched.
• the etching liquid is permeated into the interface between the gate electrode 9 and the gate insulation film 8, which makes the channel width of a TFT device smaller than the actually designed value.
• the resist is stripped and an IZO film having a thickness of 250 nm is formed as a drain electrode and a source electrode by reactive sputtering on the uppermost surface of the upper side of the substrate 4.
• the resist layer 3 is patterned on the surface of the IZO film as an etching mask by photolithography.
• the IZO film is etched to form the drain electrode 5 and source electrode 6.
• the contact pad of the gate electrode layer 9 IGO is exposed as described above, to be brought into close contact with the IZO film.
• the selective etching of IZO to IGO is required.
• the etch selectivity of IZO to IGZO is about 14.8, and the etch selectivity of IZO to IGO is about 56. That is, using the etching liquid containing citric acid, selective etching of the drain electrode layer 5 (IZO) and source electrode layer 6 (IZO) to the active layer 7 (IGZO) and simultaneously to the gate electrode layer 9 (IGO) can be performed. However, if an etching liquid having no selectivity is used in this stage, the gate electrode 9 is etched.
• the etching liquid is permeated into the interface between the gate electrode 9 and gate insulation film 8 which makes the channel width of a TFT device smaller than the actually designed value.
• the active layer 7 is also etched, and the etching liquid is permeated into the interface between the drain electrode 5 and source electrode 6, and active layer 7.
• the channel length of a TFT device becomes larger than the actually designed value .
• drain electrode layer 5 and source electrode layer 6 are formed by the lift-off process in this stage, there is posed the problem that when the photoresist is stripped, an edge of a pattern ' of a deposited film is curved up, and thereafter an electric wire crossing over the pattern edge is liable to be broken.
• the resist layer 3 is stripped with acetone .
• a bottom-gate top-contact thin film transistor is obtained in which all the electrode and active layers are formed of oxide films containing indium (IZO drain electrode layer 5, IZO source electrode layer 6, IGZO active layer 7, and IGO gate electrode 9) .
• the present invention can provide a highly selective etching method of oxide semiconductor films containing
• Ga, and Zn and formed on a substrate, and also can form semiconductor devices having stable and uniform electrical characteristics on a substrate.
• a TFT in which a transparent oxide film is used as an active layer can be applied onto a soft plastic film, and also can be applied to the fields of pixel drivers of flexible displays, IC cards for authentication, product

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